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Note for Operating Systems - OS by Abhishek Kumar

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www.Vidyarthiplus.com Operating Systems Lecture Notes Prepared By P.PARVATHI, Asst.Professor/CSE SUDHARSAN ENGINEERING COLLEGE Sathiyamangalam 622 501, Pudukkottai District. Department of Computer Science & Engineering OPERATING SYSTEMS LECTURE NOTES Prepared by P.Parvathi Assistant Professor Dept.of CSE 1 www.Vidyarthiplus.com

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www.Vidyarthiplus.com Operating Systems Lecture Notes Prepared By P.PARVATHI, Asst.Professor/CSE PROCESSES AND THREADS UNIT-I Chapter-1 Introduction What is an Operating System?  A program that acts as an intermediary between a user of a computer and the computer hardware. Operating system goals: o Execute user programs and make solving user problems easier. o Make the computer system convenient to use. Use the computer hardware in an efficient manner.   The Evaluation of Operating Systems: 1.Mainframe Systems    Simple batch systems Multiprogrammed batch systems Time-sharing systems Simple Batch Systems     User prepare a job and submit it to a computer operator User get output some time later No interaction between the user and the computer system Operator batches together jobs with similar needs to speedup processing Task of OS: automatically transfers control from one job to another.     OS always resident in memory Disadvantages of one job at a time: CPU idle during I/O I/O devices idle when CPU busy Memory Layout for a Simple Batch System 2 www.Vidyarthiplus.com

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www.Vidyarthiplus.com Operating Systems Lecture Notes Prepared By P.PARVATHI, Asst.Professor/CSE Multiprogrammed Batch Systems:    Keep more than one job in memory simultaneously When a job performs I/O, OS switches to another job Increase CPU utilization  All jobs enter the system kept in the job pool on a disk, scheduler brings jobs from pool into memory OS Features Needed for Multiprogramming:      Job scheduling: which jobs in the job pool should be brought into memory? Memory management: the system must allocate the memory to several jobs. CPU scheduling: choose among jobs in memory that are ready to run. Allocation of devices: what if more than one job wants to use a device? Multiple jobs running concurrently should not affect one Another Memory Layout for a Multiprogrammed Batch Systems Time-Sharing Systems:    Like multiprogrammed batch, except CPU switches between jobs occur so frequently that the users can interact with a running program User give instructions to the OS or a program, and wait for immediate results Require low response time 3 www.Vidyarthiplus.com

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www.Vidyarthiplus.com Operating Systems Lecture Notes Prepared By P.PARVATHI, Asst.Professor/CSE   Allow many users to share the computer simultaneously, users have the impression that they have their own machine CPU is multiplexed among several jobs that are kept in memory and on disk OS Features Needed for Time-Sharing    Job synchronization and communication Deadlock handling File system 2.Desktop Systems: Personal computers : computer system dedicated to a single user.  CPU utilization not a prime concern, want maximize user convenience and responsiveness.  Can adopt technologies developed for mainframe operating systems: virtual memory, file systems, multiprogramming  File protection needed due to interconnections of computers  Operating systems for PCs: Windows, Mac OS, Linux Multiprocessor Systems 3.Multiprocessor Systems:    Also known as parallel systems or tightly coupled systems More than one processor in close communication, sharing computer bus, clock, memory, and usually peripheral Devices Communication usually takes place through the shared memory. Advantages:    Increased throughput: speed-up ratio with N processors < N Economy of scale: cheaper than multiple single-processor systems Increased reliability: graceful degradation, fault tolerant Types of Multiprocessor Systems: a.Symmetric multiprocessing (SMP):    Each processor runs an identical copy of the operating system. All processors are peers: any processor can work on any task OS can distribute load evenly over the processors. 4 www.Vidyarthiplus.com

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